Actually , n - s equation has three unknown functions u , v , p and three equations , now prandtl boundary layer equation has two unknown functions w , vand two equations only , and viscosity terms has partly reduced 原來有三個未知函u , v , p及三個方程,現在只有兩個未知函數u , v及兩個方程,且粘性項也少了一些,這些都是簡化的地方。